1. Field of the Invention
The present invention relates to a method for laying out power supply wiring conductors in integrated circuits, and more specifically to a method for laying power supply wiring conductors so as to obtain a desired LSI functions by means of automatic laying and wirings of function blocks.
2. Description of Related Art
In the prior art, in order to realize desired LSI functions such as gate arrays, standard cells, and the like on a silicon substrate, automatic locating and wirings of function blocks have been known. However, the wirings of power supply wiring conductors have not so been automatized as in a signal line automatic treatment (which includes the locating of function blocks and interconnections of signal lines between terminals of the laid-out function blocks), for example, the gate array is excluded from the subject of the automatic wiring, and it has been handled as a wired block in which wiring conductors have been previously prepared and wired before the function block is located. In addition, some of the standard cells have been made to have such a structure that if function cells are arranged in the form of a linear array, power supply conductors are interconnected as a matter of course, and the function cells are connected at one end or at opposite ends of the linear array to power supply lines or pads.
However, with recent advances having realized an increased integration density and an increased operation speed due to microminiaturization of devices, distribution of consumed electric power on a chip surface has changed so that a diagram of the distribution extends toward a large consumed electric power side. As a result, in the method for laying out the previously prepared wiring conductors independently of the consumed electric power distribution in the inside of the chip, or in the method of simply connecting the wiring conductors of the same conductor width, an actual current sometimes exceed a bearable current capacity of the wiring conductor. This results in lowered reliability, particularly from the viewpoint of electromigration, and therefore, is very undesirable. In this connection, it may be considered to widen the power supply wiring conductors so that the maximum level of the consumed electric power distribution can be satisfied anywhere within the chip. However, this results in that, in a region of a small consumed electric power, the power supply wiring conductors have an excessive conductor width, which will remarkably decrease an area utility efficiency.
Therefore, a method for adjusting the width of the power supply wiring conductors is desired. However, it can be generally said that, in order to lay the power supply wiring conductors, it is required to ensure necessary space. For this purpose, when the functions blocks are automatically located and wired, routes and spaces for laying the power supply wiring conductors must be simultaneously taken into consideration.
However, conventional automatic locating and wiring tools have no function capable of satisfying the above mentioned demand. Besides, the conventional automatic locating and wiring tools still have many remaining problems in connection with only effective execution of automatic connection of signal lines.
Accordingly, from the viewpoint of software development, a further lead is imposed to add, to the existing functions of the automatic locating and wiring tools, a procedure which effectively performs various processings to decide location of function block, to calculate distribution of a consumed electric power, to decide laying routes and widths of power supply wiring conductors, to modify the previously decided location of function blocks so as to ensure a space for laying the power supply wiring conductors, to calculate distribution of a consumed electric power, again, and to adjust the widths of power supply wiring conductors. In addition, this may obstruct the improvement of various problems in connection with the conventional automatic connection of signal lines, and rather, may sacrifice automatic locating and wiring means which have been considered to be good in the prior art.